The general concept of patterned deposition of a material onto a substrate has many applications. Some methods of patterned deposition are additive and others are subtractive. Additive methods deposit the material only where desired. In contrast, subtractive methods deposit the material and then selectively remove (subtract) the material exclusive of the desired pattern.
One application of patterned deposition is the patterned deposition of toner particles to reproduce images. Patterned deposition may also be used to deposit patterns of different colored phosphors to form color pixels on the screen of a cathode ray tube (CRT).
Shadowing is an additive method for depositing a pattern of a material onto a substrate. For shadowing, a shadow mask is formed above or on the substrate. The material is then directionally deposited onto the substrate through apertures in the shadow mask. As a result of the deposition being directional, the material is not deposited in the "shadows" of the structure. Thus, the material is deposited in a pattern defined by the portion of the substrate exclusive of the "shadows" and the structure. By varying the direction of deposition, this technique may be used to deposit different patterns of one or more different materials on a single substrate.
Another method of patterned deposition uses a patterned photoconductor to electrostatically attract charged particles of a material onto a pattern on a substrate. For example, as used in photocopiers, a photoconductor is first applied to the substrate. The photoconductor is then electrostatically charged. The charged photoconductor on the substrate is exposed to light in a desired pattern to selectively discharge the photoconductor. Particles of the material (toner), charged to an opposite polarity than the charge of the patterned photoconductor, are brought into proximity with the substrate. The attraction between opposite charges results in the deposition of the toner onto the substrate in the pattern formed by the charged photoconductor. Paper is then brought in contact with the substrate to deposit the patterned toner onto the paper. The paper may then be heated to fuse the toner to the paper.
Another method of patterned deposition may be used for forming patterns of different colored phosphors corresponding to different colors in pixels on the screen of a cathode ray tube (CRT). For example, a photoconductor may be deposited on the screen and then charged. The photoconductor may then be selectively exposed to form a pattern of charge. Oppositely charged phosphor particles of a first color are then formed. Electrostatic attraction causes the phosphor particles of the first color to attach to the screen positions where the charges were selectively deposited. The phosphors may then be secured to the screen by curing. The process may then be repeated to form patterns of additional colors of phosphor on the screen.
For some applications and for some materials it may be desirable to deposit a pattern while the material is in liquid form. Inkjet technology may be used to deposit a liquefied material in a pattern formed by a plurality of positions on a substrate. First, the liquefied material is supplied to the inkjet. The inkjet and the substrate are then positioned so the inkjet output is adjacent one of the plurality of positions on the substrate. The material in the inkjet is then discharged toward the one of the plurality of positions on the substrate. The inkjet is then repositioned and the process is repeated for each of the plurality of positions on the substrate.
The cost and complexity of an inkjet apparatus may increase when the positions on the substrate are small and when the deposition of material must be localized. Material discharged from an inkjet typically disperses once it exits from the inkjet. To localize deposition, the extent of dispersion may be limited by precisely locating the inkjet close to the substrate.
An inkjet method may also be costly when the number of positions on the substrate is large. When material is to be deposited on many distinct positions on the substrate, using an inkjet is costly due to the time necessary to reposition the inkjet in relation to the substrate for deposition at each of the positions. Alternatively, multiple inkjets may be used to simultaneously deposit material at more than one position. This alternative may be cost prohibitive due to the cost of the multiple ink jets and their operating and maintenance costs.
Inkjet deposition of a liquid may be undesirable for depositing a precise quantity of material. After repeated discharges, an inkjet may begin to clog. A clogged inkjet may not discharge as much material as an unclogged inkjet. Thus, the amount of material per discharge may vary from position to position on the substrate, depending on the extent to which the inkjet is clogged at the various positions.
To overcome the shortcomings of conventional methods of patterned deposition, a new method of deposition is provided.